One of the eternal complaints about short range wireless is its limited range, particularly when used within homes. Whilst the name “short range wireless” ought to give a clue about the existence of the problem, it doesn’t stop a general level of indignation when a radio signal doesn’t make it through the walls of your house.

Up until now this was mostly an annoyance, largely because it was a personal problem. By that I mean it was an inconvenient truth that individuals discovered when they bought a consumer wireless product, whether that was a Wi-Fi access point, a cordless phone or a mobile headset. As these were generally low cost, discretionary purchases, users either took them back, put them in a cupboard and forgot about them, or worked around the problem by moving the appropriate access point. For the more technically engaged, a raft of companies grew up making repeaters, range extenders, power amplifiers and directional antennae, allowing users to exacerbate the problem by swamping all of their neighbours’ installations.

In the last year people have started to take the middle word of “short range wireless” rather more seriously. That’s come about as governments around the world have mandated deployments of smart meters. Whilst no-one cared too much if a consumer product didn’t work, smart meters are a different kettle of fish. They need to be able to connect with the other components of the smart metering wireless network in the home in order to send consumption data back to the utilities. They have to do that reliably and regularly over a period of many years. And they need to be able to cope with a wide variety of homes – from small bungalows to multi-storey apartment buildings. All of a sudden that “range” word is getting a lot of attention.

The problem is that the wireless standards being considered don’t cover 100% of different homes. Any one standard probably struggles with covering much more than 75% of potential homes. That’s a big problem for regulators and civil servants who have a very black and white view of life – when a mandate says “all”, they assume that means every last home. So what can they do?

In an ideal world the governments who are mandating smart metering should have started to think about the problem ten years ago. That would have given them time to release an appropriate chunk of RF spectrum and work with standards groups to define a suitable protocol. Needless to say, they didn’t, which gets us to where we are today with a raft of competing short range wireless standards all arguing that they have the best solution. That’s marketing weasel words; none of them do, at least in their present form. Each has made inevitable compromises between range, security, power consumption and bandwidth – that’s what wireless standards are all about (for more on which, buy the book or read some of my previous posts). It doesn’t mean that they couldn’t evolve to solve range, but that’s not been their first priority. Goverments also have another problem, which is their politics, as there are certain civil servants involved with smart metering in Europe who have very limited ideas regarding what a standard is and whether anyone is allowed to use some of them.

But range has become top of the list for governments and utilities, not least because it’s one of the easiest things to measure. Or is it? Surprisingly, very little work has been done to evaluate it. One of the best analyses comes from Australia. Australia has a particular problem in that they install meters in metal boxes on the outside of a house – something that most RF engineers refer to as a Faraday cage. The report looked at the effect this has on the range of ZigBee at 2.4GHz. Sadly the report isn’t public, but its main conclusions have been disclosed at a number of conferences, which are that the range from ZigBee devices was perfectly adequate in most homes, but that they would benefit from have an additional repeater somewhere in its middle, operating at 100mW

The main conclusion, which is that ZigBee worked most of the time, tended to get eclipsed by the predictable recommendation of upping the power, based on the old principle that if you shout louder, you’re more likely to be heard. It’s a less than valid corollary that is far more prevalent than it deserves to be and decidedly problematic in the real world.

Because adding a repeater as a solution is not as easy as it sounds. The cost of adding it is one issue, but a bigger one is how to power it? Today the only products that a utility needs to monitor your power consumption are an electricity meter and a gas meter. The electricity meter is self-powered and the gas meter has a big battery in it. If a repeater is added next to the electricity meter, where it can be powered from the main electricity supply, it does nothing to increase the range. But if it is located some distance from the meter, then the question arises of how to power it? If it plugs into a socket, what’s to stop a user unplugging it at some point? How many household products can you think of that have remained permanently on and powered for twenty years or more? And a device in the middle of the house transmitting at this power level is unlikely to endear itself to the electromagnetically sensitive members of the population. Although a technical solution, it’s not practical for large scale deployment. What the industry needs is an answer that doesn’t require the installation of extra boxes.

A much less focused piece of research is currently being undertaken by the UK government, which is looking at radio range at different frequencies for a variety of different types of house. At least they think that’s what they’re measuring. The actual trial is looking at carrier wave propagation, which is rather different. Part of the rationale behind it is to provide an evidence base for their eventual choice of HAN technology. The problem with this approach is that propagation is not the same as range. An earlier generation of physicists, notable Friis, have already evaluated propagation and discovered that the power received at an antenna decreases with the square of increasing frequency. Hence this piece of research will conclude that 2.4GHz, which is where ZigBee operates, has the poorest propagation of the frequencies being investigated.

It’s an outcome that doesn’t tell us anything much about range. Although range depends on propagation, it also depends crucially on the way a wireless standard uses that frequency. Wireless standards are designed to manipulate the properties of the transmission to extend or decrease range. They do this by employing coding gain, channel width, spread spectrum techniques, diversity, directional antennae and a host of other parameters.

Understanding this distinction is quite difficult, so let’s take an analogy, based on your car. A simplistic view of how fast your car could go would be based on the diameter of its wheels. If the axle turns at a particular angular velocity, then the speed is proportional to the wheel diameter. That’s akin to classic propagation and transmit power, where the diameter of the wheel is the equivalent of wavelength (which is inversely related to frequency) and the angular velocity of the axle turned by the engine is that of transmit power.

But that’s not how we build cars. In a real car we also have a gearbox, which adds a similar level of complexity to a car’s speed as a wireless standard does for range. With the gearbox present, for the same size wheel and engine rpm, you can drive at a wide variety of speeds. The gearbox makes appropriate compromises to maximise acceleration, torque and speed depending on which gear you select.

Even when you’ve grasped that propagation is not the same as range and has an important dependence on range, that’s still not the whole story. Even with the same standard, range is still highly variable dependant on different chips and pcb designs. There’s still a lot of black magic in RF design and these can affect the range of any individual product by an order of magnitude.

I’m not sure what the Government will deduce from this study. It may give them an indication of what percentage of homes need another technology, but I’m not convinced, as it doesn’t bring the reality of practical implementations into the study. What it will do is indicate that there is currently no holy grail. The more worrying scenario is that they will try to use it to ascribe a financial cost to a delay to allow them to develop a new standard. For example, “If 2.4GHz covers 60% of properties today, 868 MHz will cover 71% in two years time, 169 MHz would cover 83% in five years time and white space solves the problem altogether the year after I retire, how much money can be saved by sticking our collective heads in the sand and putting off smart metering? And is it enough to pay for my index linked pension?” Answers on a postcard to your local MP…

So what are the options for smart meter connectivity? Today, if the UK Government chooses ZigBee, they’re probably limited to fulfilling something between half and three-quarters of UK homes. Let’s be clear that whatever its failings, ZigBee SEP 1.1 has the security, throughput and higher layer application features in place to allow deployment to start. Plus there are multiple vendors supporting it, both at chip and device level. No other wireless standard can make that claim today. It is the pragmatic choice. Any limitation around range is not an excuse for delay. Over the eight or more years it will take to complete the smart metering roll-out in the UK technology will evolve and should be directed towards finding solution for the remaining proportion of homes. Hence I’d suggest that governments take a pragmatic approach. That means accepting that no solution available today will cover 100% of home, but start with one that does, then concentrate resource on adding in other technologies to fill in the missing 25-50%.

Under that plan, stage one would be to take ZigBee and target homes where it is going to work. There’s an interesting corollary to that. Homes where it will work are likely to be clustered together, where all of them have the same, or very similar construction. That means that it would make sense to start installing smart meters on a street by street basis. What’s interesting is that’s exactly what the recent Centre for Sustainable Energy report on smart metering recommended. Not for any reason of radio range, but because of the community advantages that occur when groups of people make changes together. That’s just good behavioural psychology. So let’s do that – kill two birds with one stone by starting with the streets which have houses which work with ZigBee, which will keep everyone busy for the first few years of the deployment. Then expand the smart metering deployment to other homes as new technologies appear.

As the utilities are doing this, the UK government should be looking at what comes next, to cover the next tranche of installations. One option is to use Powerline communications for properties where that’s appropriate. The Homeplug Alliance has been working with the ZigBee Alliance for several years on ensuring compatibility at an application level. It has limitations, particularly for the mobility of In Home Displays, but it can provide a solution for another group of homes.

Slightly further out, there will be time to consider a better radio for ZigBee. Currently ZigBee uses a radio defined by the 802.15.4 standard, in a version which was ratified back in 2003. Although the 802.15.4 standard has evolved in the last nine years, ZigBee hasn’t incorporated any of these upgrades, as it takes considerable time and money to develop new chips. But over the time of the smart metering deployment, it should be possible to develop a new generation of radios which could have an enhanced link budget, giving them better range. There’s quite a good chance that they could be backwardly compatible, making life easier for consumers and equipment vendors. That would probably provide a solution which would cope with the majority of detached, semi-detached and terraced homes, which covers a large portion of the UK housing stock.

It still leaves the issue of multi-story buildings, which are particularly resistant to short range wireless, particularly if the meter is in the basement. However, the issue of radio propagation in these buildings isn’t one that’s limited to ZigBee and smart metering. It’s a similar concern for mobile operators, as buildings that don’t work well for ZigBee are generally equally ill-disposed to cellular networks. Which means it’s a problem that network operators need to solve too. Recent research claims that over 75% of mobile calls are made from inside buildings, and around 95% of data access is also done inside. (That last figure’s not actually that surprising, as most data access from a mobile involves looking at your phone’s screen – an activity that’s closely correlated to walking into lampposts if you’re outside the home.)

A lot of research is going into solving this problem, notably by covering these buildings with distributed systems, capable of RF distribution over Ethernet or structured cabling. This allows RF signals over the 500MHz – 5GHz range to be distributed throughout the entirety of the building. Today most of these projects are in the research stage, although companies like Zinwave are beginning to turn them into real products. But with investment and commitment, they should appear as viable commercial solutions in the next five years. The beauty of this approach is that it would work with the current generation of ZigBee products, and it might even get paid for by the network operators.

The important thing is that we don’t wait until there is a perfect solution that covers 100% of homes. If we do, we’ll never get there, as there will be no income for the industry to evolve new solutions. Instead we need to be pragmatic. Understand the limitations and start with what we can do. And then use the experience and revenue from that to extend to new solutions. There are already roadmaps and research which promise tenable answers, but they need the momentum of deployment to bring them to reality. By working with mobile networks to solve shared problems the industry can probably move much faster. Just look at the developments in mobile infrastructure over the last decade. It shows what can be done when the commercial incentive is there.

Most importantly, don’t give in to the inherent risk aversion of the energy industry. They are facing a massive step change in their level of technology and IT systems by signing up to meet the UK smart metering mandate. Because of its degree of deregulation, the UK deployment will be one of the most complex systems in the world. The utilities are starting to realise that and some would not be averse to applying the brakes to wait for the perfect solution. Particularly if they believe that might be a long way away.

But it should all be possible. If we’re pragmatic and work together, the UK will gain some world beating expertise. Technology will get there. Eight years ago (the equivalent of how long we are planning to take to complete the UK roll-out), ZigBee was little more than a pipe dream. Wi-Fi didn’t exist, nor did the iPhone or the Pad. Technology can move faster than we realise, particularly when it has something driving it. In this case that’s a well-defined problem, with the added incentive of deploying tens of millions of real products.

The UK has taken an aggressive stance in defining and mandating the world’s most complex smart metering system. It should show its resolve in moving forward by taking the risk and stepping up to develop the appropriate new technologies alongside that deployment. If it does, then UK plc will gain valuable expertise in demonstrating and selling smart metering to the rest of the world.

Leave a Comment

Name

Mail

Website

About Creative Connectivity

Creative Connectivity is Nick Hunn's blog on aspects and applications of wireless connectivity. Having worked with wireless for over twenty years I've seen the best and worst of it and despair at how little of its potential is exploited.

I hope that's about to change, as the demands of healthcare, energy and transport apply pressure to use wireless more intelligently for consumer health devices, smart metering and telematics. These are my views on the subject - please let me know yours.

Essentials of Short Range Wireless

A helping hand for wireless designers

Adding wireless connectivity to a product is a major challenge for any designer. There are so many new concepts, and a plethora of suppliers claiming they’ve solved them for you. I’ve tried to distil 20 years of experience into this book to help you get over the pitfalls, ask the right questions and make sure you understand the answers.